We are studying microbes associated with leaves. A. pullulans is a polymorphic fungus with a life cycle involving blastospores, hyphae, chlamydospores and intermediate forms. The aims of our present studies are detection, quantification, and analysis of colonization patterns of A. pullulans associated with apple leaves by the GUS marker system and species-specific fluorescent oligodeoxynucleotide probes. We will be using the confocal microscope at the IMR to visualize the labeled fungus.